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World Bank & Government of The Netherlands funded

Training module # WQ -04

How to prepare standard solutions

New Delhi, May 1999

CSMRS Building, 4th Floor, Olof Palme Marg, Hauz Khas,New Delhi – 11 00 16 IndiaTel: 68 61 681 / 84 Fax: (+ 91 11) 68 61 685E-Mail: [email protected]

DHV Consultants BV & DELFT HYDRAULICS

withHALCROW, TAHAL, CES, ORG & JPS

Hydrology Project Training Module File: “ 04 How to prepare standard solutions.doc” Version 05/11/02 Page 1

Table of contents

Page

1 Module context 2

2 Module profile 3

3 Session plan 4

4 Overhead/flipchart masters 6

5 Evaluation sheets 16

6 Handout 18

7 Additional handout 22

8 Main text 23


1 Module context

This module describes procedure and a laboratory exercise for preparation of standardsolutions. Modules in which prior training is required to complete this module successfullyand other available, related modules in this category are listed in the table below.

While designing a training course, the relationship between this module and the others,would be maintained by keeping them close together in the syllabus and place them in alogical sequence. The actual selection of the topics and the depth of training would, ofcourse, depend on the training needs of the participants, i.e. their knowledge level and skillsperformance upon the start of the course.

No. Module title Code Objectives1 Basic water quality concepts WQ -01 • Discuss the common water quality

parameters• List important water quality issues

2 Basic chemistry concepts WQ -02 • Convert units from one to another• Discuss the basic concepts of

quantitative chemistry• Report analytical results with the

correct number of significantdigits.

3 The need for good laboratorypractices

WQ -03 • Apply the adopted standardpractices in laboratory operations


2 Module profile

Title : How to prepare standard solutions

Target group : As per training need

Duration : One session of 150 min

Objectives : After the training the participants will be able to:• Select different types of glassware• Use an analytical balance and maintain it.• Prepare standard solutions.

Key concepts : • Volumetric glassware• Analytical balance• Primary and secondary standard solutions

Training methods : Explanations, demonstration of equipment and practicalexercises.

Training toolsrequired

: • Volumetric glassware: graduated flask, pipettes, burette,graduated cylinder.

• Analytical balance with operation manual.• Required chemicals, dried, cooled and stored in

desiccator.• Support of a basic chemical laboratory.

Handouts : As provided in this module

Further readingand references

: • Analytical Chemistry: An introduction, D.A. Skoog and D.M. West/1986. Saunders College Publishing

• Chemistry for Environmental Engineering, C.N. Sawyer,P.L. McCarty and C.F. Parkin. McGraw-Hill, 1994


3 Session planNo Activities Time Tools1 Preparations

• Use your standard ToT checklist• Make sufficient copies of supplier’s instruction

manual for the available balance/s• Dry and cool beforehand sufficient quantity of

potassium dichromate and ferrous ammoniumsulphate

• Collect and arrange glassware mentioned inthe text

• Obtain ferroin indicator2 Introduction:

• Describe session context and activities• Ask the participants to read the handout

5 minOHS

3 Glassware• Demonstrate and explain salient features of

different type of glassware and their correctuse.

• Explain:− Temperature specifications− meniscus and how to read− to ‘deliver’ and to ‘contain’ specifications− rinsing of pipettes and burettes with

solutions to be transferred− holding of burette stopcock

10 minRequiredglasswarehandoutOHS

4 Analytical balance• Explain features of the balance• Ask each participant to read the operation

manual for the balance and precautions givenin the text.

• Explain the use of the available balance (twopan, single pan-mechanical or electronic) withthe help of the supplier’s instruction manual

• Demonstrate how to weigh a light object• Discuss results of the exercise• Explain balance maintenance

30 min AnalyticalbalanceOperationmanualhandoutOHS

5 Standard solutions• Explain

− the need for heating and cooling ofchemicals before weighing

− purity and different grades of chemicals

10 minHandoutOHS

6 Preparing standard solutions• Describe the steps involved• Demonstrate the titration procedure for

secondary standard

20 minHandout


7 Practice:• Divide the class in working groups of two

persons each.• Let each group prepare the standard

solutions

65 min

8 Wrap up:• Clarify doubts

10 min


4 Overhead/flipchart mastersOHS format guidelines

Type of text Style Setting

Headings: OHS-Title Arial 30-36, Bold with bottom border line (not:underline)

Text: OHS-lev1OHS-lev2

Arial 26,Arial 24, with indentmaximum two levels only

Case: Sentence case. Avoid full text in UPPERCASE.

Italics: Use occasionally and in a consistent way

Listings: OHS-lev1OHS-lev1-Numbered

Big bullets.Numbers for definite series of steps. Avoidroman numbers and letters.

Colours: None, as these get lost in photocopying andsome colours do not reproduce at all.

Formulas/Equations

OHS-Equation Use of a table will ease alignment over morelines (rows and columns)Use equation editor for advanced formattingonly


Required glassware

• Volumetric flask

• Watch glass

• Glass funnel

• Reagent bottle

• Pipette

• Burette

• Graduated cylinder

• Conical flask


Analytical balance• Capacity: 150 – 200 g

• Least count: 0.1 mg

• Care in operation

- do not exceed capacity

- beam arresting mechanism

- use tongs / forceps

- protect from hot / corrosive substance

- cleaning after every use

- vibration free table


Primary standard: preparation• Potassium dichromate solution 0•0417 M

- Use primary grade / analytical reagent grade chemical.

- Molecular Weight (MW) of K2Cr2O7 = 294g.

- weight of reagent for 1L of 0.0417M solution

g mole= 294 -------- x 0•0417 -------- x 1 L = 12•2598 g

mole L


Primary standard: procedure1. Chemical dried at 103-105 o C for 2 h & cooled in desiccator.

2. Weigh 12•2598 g in a clean, oven dried, cooled & tared watchglass.

3. Carefully transfer weighed chemical to a funnel placed on 1Lvolumetric flask.

4. Wash the watch glass with a small amount of water into thefunnel.

5. Add about 0.5L distilled water, swirl to dissolve & make up to1L mark.

6. Store the reagent in a reagent bottle (not in volumetric flask).


Secondary standard: preparation• Ferrous ammonium sulphate solution 0•25 M

- Use primary grade / analytical reagent grade chemical.

- Molecular Weight (MW) of Fe(NH4)2(SO4)2.6H2O = 392 g.

- weight of reagent for 1L of 0.25M solution

g mole= 392 -------- x 0•25 -------- x 1 L = 98 g

mole L


Secondary standard: procedure1. Weigh 98g in a clean, oven dried, cooled & tared watch

glass.

2. Carefully transfer weighed chemical to funnel placed on a 1Lvolumetric flask.

3. Wash watch glass & funnel with distilled water into flask using wash bottle.

4. Add about 0.5 L distilled water & 20 ml concentrated H2SO4,cool and dilute to 1L mark.

5. Store reagent in reagent bottle (not in volumetric flask).


Standardisation

• Standardise Ferrous ammonium sulphate solution againststandard potassium dichromate solution, 0.0417M as follows:

1. Dilute 10mL standard K2Cr2O7 to about 100 mL in a conical flask.

2. Add 30 mL conc. H2SO4 and cool.

3. Add (2 to 3 drops) ferroin indicator.

4. Titrate with FAS titrant using 0.10 to 0.15mL

5. Read volume when solution turns red at end point

6. Calculate molarity


Calculate molarity: Ferrous ammonium sulphate

Vol. of 0.0417M K2Cr2O7 solution tritrated, mL

Molarity = ------------------------------------------------------------------ x 0.25

Vol. of FAS used in titration, mL


Exercise

Prepare standard solutions

• Work in groups of two

• Time 65 min


5 Evaluation sheets


6 Handout


Required glassware• Volumetric flask• Watch glass• Glass funnel• Reagent bottle• Pipette• Burette• Graduated cylinder• Conical flask

Analytical balance

• Capacity: 150 – 200 g• Least count: 0.1 mg• Care in operation

- do not exceed capacity- beam arresting mechanism- use tongs / forceps- protect from hot / corrosive substance- cleaning after every use- vibration free table

Primary standard: preparation

• Potassium dichromate solution 0.0417 M- Use primary grade / analytical reagent grade chemical.- Molecular Weight (MW) of K2Cr2O7 = 294g.- weight of reagent for 1L of 0.0417M solution

g mole= 294 -------- x 0.0417 -------- x 1 L = 12.2598 g

mole L

Procedure1. Chemical dried at 103-105 o C for 2 h & cooled in desiccator.2. Weigh 12.2598 g in a clean, oven dried, cooled & tared watch glass.3. Carefully transfer weighed chemical to a funnel placed on 1L volumetric flask.4. Wash the watch glass with a small amount of water into the funnel.5. Add about 0.5L distilled water, swirl to dissolve & make up to 1L mark.6. Store the reagent in a reagent bottle (not in volumetric flask).

Secondary standard: preparation• Ferrous ammonium sulphate solution 0.25 M- Use primary grade / analytical reagent grade chemical.- Molecular Weight (MW) of Fe(NH4)2(SO4)2.6H2O = 392 g.- weight of reagent for 1L of 0.25M solution

g mole= 392 -------- x 0.25 -------- x 1 L = 98 g

mole L


Secondary standard: procedure

1. Weigh 98g in a clean, oven dried, cooled & tared watch glass.2. Carefully transfer weighed chemical to funnel placed on a 1L volumetric flask.3. Wash watch glass & funnel with distilled water into flask using wash bottle.4. Add about 0.5 L distilled water & 20 ml concentrated H2SO4, cool and dilute to 1L

mark.5. Store reagent in reagent bottle (not in volumetric flask).

Standardisation

• Standardise Ferrous ammonium sulphate solution against standard potassiumdichromate solution, 0.0417M as follows:

1. Dilute 10mL standard K2Cr2O7 to about 100 mL in a conical flask.2. Add 30 mL conc. H2SO4 and cool.3. Add (2 to 3 drops) ferroin indicator.4. Titrate with FAS titrant using 0.10 to 0.15mL5. Read volume when solution turns red at end point6. Calculate molarity

Calculate molarity: Ferrous ammonium sulphate

Vol. of 0.0417M K2Cr2O7 solution tritrated, mLMolarity of FAS solution = ------------------------------------------------------------------ x 0.25


Exercise: Prepare standard solutions• Work in groups of two• Time 65 min


Add copy of Main text in chapter 8, for all participants.


7 Additional handoutThese handouts are distributed during delivery and contain test questions, answers toquestions, special worksheets, optional information, and other matters you would not like tobe seen in the regular handouts.

It is a good practice to pre-punch these additional handouts, so the participants can easilyinsert them in the main handout folder.


8 Main text

Page

1. Aim 1

2. Basic glassware 1

3. Analytical balance 1

4. Glassware required for practicalexercise 1

5. Preparation of primary standard,potassium dichromate solution,0.0417M 1

6. Preparation of secondary standard,ferrous ammonium sulphate,approximately 0.25M 2


How to prepare standard solutions

1. Aim2. To become familiar with basic glassware and equipment3. To learn use and care of the chemical balance4. To prepare standard solutions

(a) Primary standard 0.0417 M K2Cr2O7

(b) Secondary standard ferrous ammonium sulphate (FAS), approximately 0.25 M

2. Basic glasswareVolumetric or graduated flask. Pear shaped flat bottom vessel with a long neck. A lineetched around the neck indicates the specified volume it contains when filled to the mark.Used for preparation of standard solutions and exact dilutions.

Pipettes. There are two kinds: (1) those which have one mark and deliver a small constantvolume; (2) those in which the stem is graduated and deliver various small volumes at theuser’s discretion. Used to transfer exact volumes.

Burette. Long cylindrical tube of uniform bore throughout the graduated length, terminatingat the lower end in a stopcock. Used to add increasing amounts of solutions in exactvolumes as in titration.

Graduated cylinder. Graduated cylindrical tubes used to measure and transfer liquidvolumes where a high level of accuracy is not required.

3. Analytical balanceUsed for weighing chemicals for the preparation of solutions. Common balances have aweighing capacity of 150 and 200 g and can read down to 0.1 mg.

The maximum weighing capacity should not be exceeded. Be certain that the arrestingmechanism of the beam is engaged whenever the loading of the balance is being changedand when the balance is not in use. Tongs or forceps should be used to place or removearticles from the pans. Never weigh hot or corrosive substance that is likely to damage thebalance. Clean the balance after every use.

4. Glassware required for practical exerciseVolumetric flask, watch glass, glass funnel, reagent bottle, pipette, burette, graduatedcylinder, conical flask.

5. Preparation of primary standard, potassium dichromatesolution, 0.0417M

1. Use primary grade or analytical reagent grade chemical for the preparation of thestandard solution. The chemical should be dried at 103-105 o C for 2 h and cooled in adesiccator.

2. Molecular Weight (MW) of K2Cr2O7 = 294g. Therefore weight of reagent for 1L of0.0417M solution = 294g/mole x 0.0417 mole/L x 1L = 12.2598 g.

3. Weigh the above amount into a clean, oven dried, cooled and tared watch glass.4. Carefully transfer the weighed chemical to a funnel placed on a 1L volumetric flask.5. Wash the watch glass with a small amount of water into the funnel.6. Add about 0.5L distilled water, swirl to dissolve and make up to 1L mark.


7. Store the reagent in a reagent bottle (not in the volumetric flask).

6. Preparation of secondary standard, ferrous ammoniumsulphate, approximately 0.25M

1. Molecular Weight (MW) of Fe(NH4)2(SO4)2.6H2O = 392 g. Therefore weight of reagentfor 1L of 0.25M solution = 392 g/mole x 0.25 mole/L x 1L = 98 g.

2. Weigh the above amount into a clean, oven dried, cooled and tared watch glass.3. Carefully transfer the weighed chemical to a funnel placed on a 1L volumetric flask.4. Wash the watch glass and the funnel with distilled water into the flask using a wash

bottle.5. Add about 0.5 L distilled water and 20 ml concentrated H2SO4, cool and dilute to 1L

mark.6. Store the reagent in a reagent bottle (not in the volumetric flask).7. Standardise this solution against standard potassium dichromate solution, 0.0417M as

follows:

Standardization

Dilute 10mL standard K2Cr2O7 to about 100 mL in a conical flask. Add 30 mL conc. H2SO4

and cool. Titrate with FAS titrant using 0.10 to 0.15mL (2 to 3 drops) ferroin indicator. Thesolution turns red at the end point.

Vol. Of 0.041M K2Cr2O7 solution tritrated, mLMolarity of FAS solution = ------------------------------------------------------------- x 0.25


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